Upgrade page fixes (rebased onto develop)



This is the same as gh-263 but rebased onto develop.

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This was discussed with @ctrueden and @sbesson in devteam on the evening of 22 February.

@ctrueden also suggested changing the formatting of the default/placeholder db names and credentials, so that it's more obvious what needs to be replaced.  Happy to do that here if @hflynn thinks that's a good plan; just let me know how best to accomplish it.